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2–3 min, up to 3–5 min on heavy singles to sixes — ACSM 2009, evidence category B
3:00
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At least 2–3 minutes between sets of core exercises with heavier loads, and 1–2 minutes for assistance exercises. The same stand puts 3–5 minutes on the 1–6 RM loading it recommends for advanced lifters.
Those intervals come from the American College of Sports Medicine’s 2009 position stand on progression in resistance training, and each carries the evidence grade the ACSM gave it — the power row is graded D, meaning panel opinion rather than trial evidence, and it is labelled that way rather than presented as settled.
The countdown is worked out by subtracting timestamps, not by counting ticks, so it stays correct when a phone dims the screen and throttles the tab. It cannot make a sound or fire a notification while it is in the background, though, so keep it in view if you need to be told.
Sets and repetitions get written down; the gap between them usually does not, and then it drifts with whatever the phone is showing. That gap changes what the session trains. Rest long enough to recover force output and you can repeat a heavy set at full quality; cut it short and the same load becomes a conditioning stimulus with a barbell attached. This is a countdown with the published intervals attached to it, so the number on the clock has a reason behind it.
The figures here are from the American College of Sports Medicine’s 2009 position stand on progression in resistance training. Heavy strength work gets at least two to three minutes between core lifts, stretching to three to five minutes on sets of one to six repetitions. Hypertrophy work gets one to two minutes, rising to two to three on heavy compound lifts for advanced trainees.
Explosive work is treated like strength work, at two to three minutes and up to five for fast multi-set training. Endurance work goes the other way: under a minute between sets of ten to fifteen, and one to two minutes once sets run past fifteen repetitions. Circuit training rests only for as long as it takes to reach the next station.
The stand attaches an evidence grade to each recommendation, and they are not equal. The strength interval is graded B, the hypertrophy and endurance intervals C, and the interval for power training is graded D — the panel’s judgement rather than trial evidence. Those grades are shown next to each figure here rather than filed away, because a number backed by opinion and a number backed by trials should not look identical on a screen.
Later work refines rather than overturns them. A 2018 systematic review by Grgic and colleagues found short and long rests both workable for untrained lifters, with longer rests favoured once someone has training history behind them.
Browsers throttle background tabs aggressively, and a timer that counts its own ticks loses minutes the moment a phone screen dims — which is exactly when it is in a pocket between sets. This one records the instant it started and subtracts, so the remaining time is correct whenever you look at it, however badly the browser behaved in between. What it cannot do in the background is make a noise, so keep it visible if you need to be told.
For repeating a genuinely heavy set at full quality, roughly that much is what the position stand recommends, and phosphocreatine resynthesis takes minutes rather than seconds. If you are training for size at a moderate load, a shorter rest costs you far less and buys back session time.
Not for strength, where the evidence points the other way — cutting rest short reduces the load you can handle on later sets and therefore the total quality work done. It does make the session longer, which is a real cost worth weighing rather than a training error.
The stand explicitly separates them and allows one to two minutes for assistance work, against two to three for core lifts under heavy loads. Curls and lateral raises do not deplete you the way a heavy squat does, and treating them identically mostly wastes time.
A few extra minutes on one set is not a problem worth worrying about, though the muscles cool and the next set may need a rebuilt approach. The larger cost is consistency: if rest varies wildly, session to session comparisons of load and reps stop meaning very much.